As subsea hydrocarbon production systems have evolved over time, certain challenges have become more problematic. One challenge is that subsea pipeline systems now traverse greater distances often at great depths. Another challenge is that certain subsea production fields necessitate installing subsea pipeline across difficult geographical formations along the seabed, including canyons, scarps and rough terrain, or in areas of high risk for geo-hazards such as mudflows, earthquakes, soil liquefaction and soil instability. Locating a pipeline in relation to such areas is of concern because it may be damaged by an impact generated by a geo-hazard, such as a mudslide or mudflow across the pipeline. A pipeline can also be damaged by fatigue due to vortex induced vibration or cyclic pipe movements due to slugging of the fluid flowing therein. Dynamic structures such as marine risers connected to platforms are susceptible to fatigue damage, as are pipeline scarp crossings with long unsupported spans. Very often these dynamic structures tend to have certain locations in which fatigue loading is more concentrated, such as sections near the touchdown point regions in steel catenary risers.
Conventionally, pipeline systems are designed to resist or withstand the forces associated with such geo-hazards. Detailed geo-hazards surveys and analyses are conducted to estimate the likelihood and severity of a geo-hazard event and associated loads on the pipeline. Current design processes, which involve multiple complex uncertainties, aim to assess the behavior of the pipeline when subject to extreme loading conditions and pursue a pipeline design that will sustain the impact forces and limit the risk of catastrophic failure. Current design mitigations include pipeline routing selection, engineered terrain excavation, horizontal directional drilling, stringent pipeline manufacturing standards, installation procedures and qualification testing, and the use of special materials, flexible elements, anchoring, and the like. These mitigations are very expensive and may have limited effectiveness to address the risks. Once there is damage to a producing pipeline leading to failure such as a rupture, current methods for containment of spills and repair solutions are limited. Pipelines, risers and scarp crossings are also often subject to operating and environmental loading, which can lead to cyclic stress in the pipe structure. This requires designing pipeline with high quality standards of fabrication to endure fatigue loads, such as tight tolerances, stringent welding standards and weld flaw acceptance criteria, limitations during installation and operation, qualification testing, etc.
It would be desirable to have an economical, reliable means for protecting subsea pipeline and riser systems from excessive loads associated with geo-hazards, environmental loading and operating loading and a response intervention method which could prevent significant production disruption. In addition it would be desirable to have a means to alleviate fatigue damage in critical regions of the pipeline and riser systems in a planned or contingency situation.